Electrolytic process



United States Patent 2,880,147; 7 I ELECTROLYTIC PROCESS George L. Cunningham, Cleveland Heights, Ohio,- asslguor to Horizons Incorporated, Princeton,- NJ., a corporation of New Jersey No Drawing; Application February 13, 1956 Serial No'. seassr 3 Claims. (Cl. 204-3 This invention relates to the electrodeposition of. metals from an aqueous bath. More particularly, it relates to a method of'electrodepositing a metal on a coated cathode from which it may be readily stripped, and to the coating applied to the cathode.

There are described in the prior art numerous processes for treating cathode surfaces to permit ready separation of the electrodeposited metal from the cathode. A number of such methods. are described in Blum and Hogaboom Principles of Electroplating and Electroforming. In general, the treatments are intended to produce a surface with the necessary bond so as to prevent premature separation of the electrodeposit from the supporting surface. Two types of treatments are described, producing either a chemical film or a mechanical film, such as a film of grease or wax in a solvent or a film of graphite from an aqueous mixture. My invention is concerned primarily with a mechanical film but unlike those previously employed, the film used by me does not readily disintegrate under the conditions present in the bath. Briefly my invention lies in the discovery that a film suitable for my purpose may be formed on a conductive electrode by coating the electrode with a composition containing, (1) a small but significant amount of a film-forming material such as ethyl cellulse,-which would ordinarily electrically insulate the cathode, and (2) a significant amount of graphite which provides the necessary conductivity to the coating. Preferably there is also included a vehicle for thinning the graphite-film former composition.

For purposes of illustration, I will describe my invention with specific reference to the electrolysis of iron, but it will be understood that what is said is equally applicable to the production of strippable electrodeposits of other metals such as copper, tin, nickel, cadmium, lead, zinc, and the like, from aqueous electrolytes.

Electrodeposition of iron is presently generally accomplished from solutions of ferrous salts, usually the chloride or sulfate. When using metal cathodes, iron, steel and Monel metal have been found suitable. In order to obtain deposits at satisfactory current efiiciencies, it is necessary, particularly when working with the chloride, to separate the anode and cathode regions of the cell from one another. For this purpose diaphragms or semipermeable membranes are often employed. I have found that when an aqueous suspension of graphite is used to coat a metal cathode, the graphite disengages itself from the cathode and tends to clog the interstices of whatever barrier is used to keep the anode and cathode regions separated.

In accordance with my invention I apply graphite to a metal cathode by means of a composition containing three ingredients, namely: graphite, a film-forming constituent and a solvent or dispersing agent.

The graphite is preferably finely ground and should be as pure as possible in order to avoid introducing impurities into the deposited metal. There are commercially availlose; styrene,. acrylates, methacryl'ates, and many others.

Any of. the usual. vehicles may be used to form athin paint ofthe graphite and ethyl cellulose. I' have found xylene to be-particularly suited for the purpose.

the particular film-forming compound employed.

The-following example will describe one specific formul'atiom although; I do; not. wish to be limited to the same-,.

since it will be obvious to others skilled in the: art that the proportions and constituents may be considerably varied without departing from the spirit of my invention.

A coating formulation was made by adding 30 grams of finely ground graphite to 264 grams of xylene and 6 grams of ethyl cellulose. The mixture was stirred and was thereafter promptly applied to a Monel metal cathode. The method of application is not critical and small cathodes may be dipped into the paint and withdrawn and the paint allowed to dry thereon. With larger cathodes, the paint may be applied as a spray or by means of a roller or brush.

A solution of ferrous chloride containing 160 to 180 grams of ferrous iron per liter was electrolyzed at between and C. for several hours using a Monel cathode coated with one coat of the graphite paint above described. Iron was deposited as a smooth sheet which was readily removed upon completion of the electrolysis.

The electrolysis was carried out with Monel cathodes, roughly 7 inches by 5 inches in area in a cell in which the anode and cathode were separated by a finely woven Vinyon cloth diaphragm. No clogging of the pores of the membrane was observed and none of the graphite appeared to become separated from the cathode. Furthermore, the electrodeposited iron did not appear to be contaminated with the graphite.

Instead of using a single coat, two or more coats of the graphite paint may be employed. In this modification, each coat of graphite paint is allowed to dry before an other is applied.

The relative proportions of the three components of the composition employed for coating metal cathodes may be varied over a wide range. The proportion of carbon to water-insoluble film-forming constituents must be such that sufficient conductivity is provided by the carbon to permit a continuous electrodeposit to be obtained. By employing a ratio of at least 2:1 parts (by volume) it is insured that a sufficient portion of the conducting particles will be presented at the surface of the coating to insure the desired conductivity. On a volume basis, preferably a ratio of 3:1 should be used. When the proportion of conductive particles is below that set forth, the water-insoluble film-forming constituent may be present in a sufficient concentration to form a continuous insulating film over the cathode and prevent the deposit of metal. While a preferred composition has been set forth above, by way of example, in which the relative proportions of the graphite: the water-insoluble film-forming compound were 5:1 by weight, these proportions may be as little as 1:1 or as great as 10:1. The amount of vehicle or solvent employed should be at least sufiicient to make the resulting composition a thin fluid at room temperature in order to facilitate the application of same to the metalcathode in the form of an adherent film coating the entire: cathode surface after evaporation of the vehicle. About7Q Patented Mar. 31, 1.959

I prefer to employ ethylcellulose as the film- Other: vehicles which may be used include: benzene, toluene, alcohols and others, the choice; depending primarily on;

air-aqueous electrolyte which includes coatinga metal- 5 cathode with a composition to facilitate the separation of the metal electrodeposit from said cathode, said composition consisting essentially of: finely divided graphite, ethyl cellulose and a compatible solvent for said ethyl cellulose, in which the relative proportions of graphite to ethyl cellulose lie between 1 to 1 and 10 to 1 and are suificientto. provide an electrically conductive coating on said cathode".

but below the amount which produces a coating lacking in adherence and the solvent constitutes between about 70% and 90% by weight of the final composition; im-

mersing said coated cathode in an aqueous electrolyte; electrodepositing metal on said coated cathode; withdraw 3. The process of claim 2 in which the composition consists of thirty parts by weight of graphite particles, six parts by weight of ethyl cellulose and two hundred sixtyfour parts by weight of xylene.

References Cited in the file of this patent UNITED STATES PATENTS 903,404 'Reverdys Nov. 10, 1908 1,037,887 Franklin Sept..10,--1912 1,206,881 Miller Dec. 5, 1916 1,866,757 De Vries -..a July 12, 1932 2,173,445 Zapp Sept. 19, 1939 2,588,625 Ferner et a1 Mar. 11, 1952 2,637,404 Bart May 5, 1953 2,682,500 Tanner June 29, 1954 FOREIGN PATENTS 14,270 Great Britain Oct. 20, 1887 16,634 Great Britain July. 3, 1896 

1. A PROCESS FOR ELECTRODEPOSITING A FERROUS METAL FROM AN AQUEOUS ELECTROLYTE WHICH INCLUDES COATING A METAL CATHODE WITH A COMPOSITION TO FACILITATE THE SEPARATION OF THE METAL ELECTRODEPOSIT FROM SAID CATHODE, SAID COMPOSITION CONSISTING ESSENTIALLY OF: FINELY DIVIDED GRAPHITE, ETHYL CELLULOSE AND A COMPATIBLE SOLVENT FOR SAID ETHYL CELLULOSE, IN WHICH THE RELATIVE PROPORTIONS OF GRAPHITE TO ETHYL CELLULOSE LIE BETWEEN 1 TO 1 AND 10 TO 1 AND ARE SUFFICIENT TO PROVIDE AN ELECTRICALLY CONDUCTIVE COATING ON SAID CATHODE BUT BELOW THE AMOUNT WHICH PRODUCES A COATING LACKING IN ADHERENCE AND THE SOLVENT CONSTITUTES BETWEEN ABOUT 70% AND 90% BY WEIGHT OF THE FINL COMPOSITION; IMMERSING SAID COATED CATHODE IN AN AQUEOUS ELECTROLYTE; ELECTRODEPOSITING METAL ON SAID COATED CATHODE; WITHDRAWING THE CATHODE FROM THE ELECTROLYTE AND REMOVING THE ELECTRODEPOSITED METAL FROM THE CATHODE. 